1. Technical Field
The present invention relates to an image capturing apparatus, an image capturing method, a storage medium, and a device control system for controlling vehicle-mounted devices.
2. Background Art
Conventionally, vehicles are equipped with an image capturing apparatus using one image sensor to capture sensing-use images for recognizing objects (e.g., other vehicles, lanes, road surface, persons, obstacles) ahead of the vehicles, and adhering-detection-use images for detecting substance such as raindrop adhering on windshields of the vehicles.
For example, conventional image capturing apparatuses capture image capturing frames (sensing frames) for acquiring thirty sensing-use images consecutively and then captures one image capturing frame (adhering detection frame) for acquiring one adhering-detection-use image, and this image capturing operation is performed repeatedly. As to the conventional image capturing apparatuses, the sensing frames are captured by automatically adjusting an exposure time by using an automatic exposure control while the adhering detection frame is captured using a locked exposure time suitable for detecting an adhering substance.
As to the conventional image capturing apparatuses that capture an image of the adhering detection frame and images of the sensing frames consecutively, a time interval of sensing frames before and after one adhering detection frame becomes longer as a frame time of the adhering detection frame becomes longer. The longer the time interval between the sensing frames, the longer the elapsed time from a time point that captures the sensing frame before the adhering detection frame to a time point that captures the sensing frame after the adhering detection frame. Therefore, situations ahead of the vehicle (e.g., relative position of objects ahead the vehicle) may change greatly between the sensing frames before and after the adhering detection frame, with which recognition precision of objects ahead the vehicle may deteriorate. Therefore, it is preferable to set the frame time of the adhering detection frame shorter as much as possible.
However, a problem occurs when the sensing frame right after the adhering detection frame is captured under the automatic exposure control while the frame time of the adhering detection frame is set shorter. Specifically, when the sensing frame right after the adhering detection frame is captured under the automatic exposure control, the exposure time of the sensing frame becomes longer under dark environment such as in a tunnel or night. The exposure time means a time period from a start of receiving the light to an end of receiving the light by light receiving elements of the image sensor of the image capturing apparatus. Since a timing of outputting received-light quantity data of each of the light receiving elements from the image sensor is pre-set, if the exposure time is set longer, the light-receiving start time becomes earlier in view of the longer exposure time.
Normally, even if the frame time of the sensing frame is set with an exposure time corresponding to an upper limit settable by the automatic exposure control, the light-receiving start time of the sensing frame does not overlap the exposure period of the previous sensing frame. However, if the frame time of the adhering detection frame is set shorter than the frame time of the sensing frame, the light-receiving start time of the sensing frame right after the adhering detection frame may overlap the exposure period of the adhering detection frame right before the sensing frame. If the overlapping of exposure periods occurs, the received-light quantity data cannot be correctly acquired for at least one of the adhering detection frame and the sensing frame right after the adhering detection frame.